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SM + Top physics Summary

SM + Top physics Summary. Marina Cobal, ATLAS Overview Week Freiburg, October 2004. Outline. Lot of activity…I had to make some selection! SM results in 2004 TGCs and AQGCs PDFs Underlying Events and Minimum bias Top results in 2004 New spin correlation studies

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SM + Top physics Summary

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  1. SM + Top physics Summary Marina Cobal, ATLAS Overview Week Freiburg, October 2004

  2. Outline • Lot of activity…I had to make some selection! • SM results in 2004 • TGCs and AQGCs • PDFs • Underlying Events and Minimum bias • Top results in 2004 • New spin correlation studies • New study on resonances • Commissioning with the top • Plans Marina Cobal - Atlas Week, Oct 2004

  3. TGCs and QGCs

  4. big advantage for LHC Triple Gauge-boson Couplings • Non-abelian SU(2)L×U(1) Y gauge group (foundation of SM!)  WWγ WWZcouplings • most-general C & P conserving WWZ,WWγ • vertices are specified by just 5 parameters: • model independent parameterization • Probe tool: sensitive to low energy remnants of new physics • operating at a higher scale • complement to direct searches L. Simic Marina Cobal - Atlas Week, Oct 2004

  5. Events selection • New study covers the purely leptonic channel: • Selection • PT>25 GeV, |η|<2.5 • ETmiss >50 GeV • Z mass constraint |MZ-Mll|<15 GeV • Veto Jets with PT(jet)>10 GeV and |η(jet)|<3 The expected number of events at 30 fb-1 is 7800, with 11% background. • Background: New!! Marina Cobal - Atlas Week, Oct 2004

  6. TGC’s in WW processes Inclusion of anomalous couplings at WWZ and WWγ vertices yields enhancements in: • s(WW) at large values in l and Dk • PT(W) or PT(e) distributions • PT(WW) or PT(e+e-) distributions NLO corrections are large in the same regions. Theoretical arguments suggest that anomalous TGC’s are at most of O (m2W/Λ2) Λ is scale of new physics. For Λ~1 TeV TGC’s are O(10-2). Marina Cobal - Atlas Week, Oct 2004

  7. Confidence intervals for TGC’s In WW processes 95% confidence intervals for TGC parameters for 30 fb -1 and ΛFF= 2 TeV are: WW processWZ and Wγ process -0.028 < ΔκZ < 0.057 -0.11 < ΔκZ < 0.12 -0.035 < λZ < 0.026 -0.0073 < λZ < 0.0073 -0.077 < Δκγ < 0.15 -0.075 < Δκγ < 0.076 -0.061 < λγ < 0.063-0.0035 < λγ < 0.0035 -0.13 < Δg1Z < 0.42-0.0086 < Δg1Z < 0.011 for HIZ (equal coupling) scheme: ΔκZ= Δκγ=ΔκλZ= λγ=λ -0.024 < Δκ < 0.025 -0.017 < λ < 0.017 WW channel will be competitive (1d fit, not systematic included) with WZ and Wγ in determining limits for ΔκV M. Dobbs,M. Lefebvre: ATL-PHYS-2002 023/022 Marina Cobal - Atlas Week, Oct 2004

  8. P. Bell Wgg : Quartic Gauge Couplings • LHC able to probe AQGCs through vector boson fusion and triple vector boson production • Wgg : good place to start looking for: • low partonic centre of mass required • suppressed by only one branching ratio • Wgg production is sensitive to possible AQGC of the form WWgg – this is SM? • Effects of AQGC on the qq to lngg with l = e or m at LHC have been studied by Eboli et al who have a MC with AQGCs implemented • Effects of AQGC can be seen on distributions of PT(g) and invariant mass of the photon pair, Mgg. Marina Cobal - Atlas Week, Oct 2004

  9. Wgg in ATLAS PTg • Consider only the exclusive channel qq to engg • Process events using ATLFAST • Cross section falls rapidly with the cut on PTg • Two photons, PT>15 geV, |n|<2.4 • One e with PT > 25, |n|<2.4 • Missing ET > 20 GeV • DRgg > 0.4, DReg > 0.8 • MT (ln)> 65 GeV • Simulation chain • Weighted events from W2GRAD • Implemented as external process in PYTHIA within ATHENA-ATLFAST • PYTHIA added beam remnants, QCD showers and underlying events and do the frag/decay etc as usual • Accept/reject alg then passes events of unit weight to ATLFAST Eboli et al Marina Cobal - Atlas Week, Oct 2004

  10. Results • Background: Wg +1 jet and W+2 jet events with one or both jets are misidentified as a g, with probability 1/Rjet (ATL-PHYS-99-016 gives Rjet=1300 @ low L, Pj = 20GeV) • 106 Wg + jet and W + 2jet events going through PYTHIA + ATLFAST • If e~ 80% for e and g, S=14 evts in 30fb-1, so about 60 for l+-ngg. Background ~ 13 evts • PTg and Mgg dist. show that the SM background and mis id can still be removed by cutting at PT = 200 GeV, so that Eboli’s conclusions hold even with these backgrounds Marina Cobal - Atlas Week, Oct 2004

  11. Feature of Wgg production In SM. Amplitude for qq Wg vanishes for cosq* = -1/3 ( angle between the q and the W in parton CMS) • This radiation is preserved in the limit of 2 collinear g’s • Vanishes as h increases  g separation criteria for detection • Independent from PT(n) and same in lab and parton frames • Dip at 0.1 for cosqgg > 0 after suppressing radiative W events • Previous selection + g opening angle requirement • Chance in 3 y, clear with 100fb-1 The Radiation Zero [1] e-negg expectation in 30fb-1 [2] [1] x 4 [3] e-negg expectation in 100fb-1 x 4

  12. PDFs

  13. Uncertainty on the PDF’s: Propagation of uncertainties on experimental data to the fitted PDF’s Statistical uncertainties and (correlated) systematic effects Uncertainties in the theoretical description of the fit procedure Flavour thresholds, s Scales uncertainties Nuclear effects Higher twist, … A number of groups have published the PDF fits with propagated experimental uncertainties: Botje(Eur Phys J C14 (dec 1999)) CTEQ (J. Pumplin et al, hep-ph/0201195) MRST (A. Martin et al, hep-ph/0211080) Alekhin (S. Alekhin, hep-ph/0011002) Fermi2001 (Giele et al, hep-ph/0104052) Theoretical uncertainties not treated here PDF’s obtained from QCD DGLAP evolution fits to data. DIS data from fixed target and HERA Jet cross sections pp colliders Drell-Yan processes Parton parameterizations Marina Cobal - Atlas Week, Oct 2004

  14. A.M. Cooper-Sarkar W+ rapidity ZEUS-S Z rapidity ZEUS-S • For LHC: fits of ZEUS and MRST02 in agreement within PDF uncertainties • Both fits use conventional NLOQCD evolution in the DGLAP formalism including data taken at very low-x (down to x=6 10 -5) • Whereas this formalism still fits the data very well, there are theoretical reasons to doubt its validity at low-x (Devenish and Cooper-Sarkar, ‘Deep Inelastic Scattering’, OUP 2004, Section 6.6.6 and Chapter 9) W+ rapidity MRST02 Z rapidity MRST02

  15. PDFs derived from a fit without low-x data : MRST03 conservative partons’. • Compare predictions for W/Z production to those of the ‘standard’ PDFs • The two predictions are very different for LHC (not so different for tevatron) • W and Z rapidity distributions for │η│< 2.4 are potentially sensitive to the treatment of low-x QCD evolution. W+ rapidity MRST02 Z rapidity MRST02 Z rapidity MRST03 W+ rapidity MRST03

  16. R = W- / W+ ZEUS-S s(W-)/s(W+)=0.75±0.02 R = W- / W+ MRST02 s(W)/s(W+)=0.74 R = W- / W+ MRST03 s(W-)/s(W+)=0.79 • The shape of the ratio of W rapidities seems well suited to NOT seeing these differences between different PDFs – minimizing PDF errors- • The magnitude of the ratio differs by ~5%. Is the luminosity error small enough to see this? Is this a good luminosity monitor?

  17. MRST02 MRST03 Suppose we WANT to see the differences ? • Differences evident for the Z rapidity distributions, once one has moved away from central rapidity. How well can we measure the Z rapidity distribution? • Need to know the efficiency of Z reconstruction for │y│> 1.2 accurately because the difference between MRST02 and MRST03 at central rapidity is mostly normalisation. • The shape differences become most evident for │y│~2 Z reconstruction efficiency vs y Similar exercise done with the W’s

  18. UE and Min Bias

  19. Min bias events • Definition depends on the experiment trigger! Usually is associated to non-single-diffractive events (NSD) – (see ISR<UA5,E735,CDF…) • Dominated by soft interactions, although there is some contributions from hard scattering σtot ~ 102 - 118 mb σNSD ~ 65 - 73mb (PYTHIA) (PHOJET) (PYTHIA) Marina Cobal - Atlas Week, Oct 2004

  20. UE in charged jet evolution • Everything except the two outgoing hard scattered jets • In a hard scattering process, the underlying event has a hard component (ISR+FSR and particles from the outgoing hard scattered partons) and a soft component (beam-beam remnants) CDF analysis: • charged particles: pt>0.5 GeV and |η|<1 • cone jet finder: Df = f - fljet Many published data: Durham HEP database JetWeb Marina Cobal - Atlas Week, Oct 2004

  21. Comparing different PYTHIA tunings to data dNchg/dη at η=0 F(z) = <nchg > P(nchg) LHC √s (GeV) z = nchg /<nchg > High-multiplicity events are described differently by each tuning Marina Cobal - Atlas Week, Oct 2004

  22. Comments: Central Region (data dNchg/dη ~ 4) Transverse < Nchg > • ATLAS – TDR: not tuned to UE data; doesn’t include double diffraction for minimum bias events; uses a model with a small hadronic core size; doesn’t correct for particle decays which affect minimum bias distributions and doesn’t include a pTmin energy dependence. dNchg/dη ~ 15 dNchg/dη ~ 10 Ratio (MC/Data) Pt (leading jet in GeV) • CDF tuning: tuned particularly to UE data; doesn’t correct for particle decays which affect minimum bias distributions. Marina Cobal - Atlas Week, Oct 2004

  23. Marina Cobal - Atlas Week, Oct 2004

  24. Data-MC Multiplicity information: ‹nch›, dN/dη, KNO Transverse region (UE): ‹nch› and ‹pTsum› Marina Cobal - Atlas Week, Oct 2004

  25. Central Region (min-bias dNchg/dη ~ 7) Transverse < Nchg > LHC dNchg/dη ~ 30 x 3 x 2 dNchg/dη ~ 20 Tevatron Pt (leading jet in GeV) LHC predictions: PYTHIA6.214 – tuned vs. CDF Tuning Marina Cobal - Atlas Week, Oct 2004

  26. LHC predictions Marina Cobal - Atlas Week, Oct 2004

  27. Summary on UE and min bias • Current min bias and UE data can be described with appropriate tuning for PYTHIA and PHOJET • PYTHIA6.214-tuned and PHOJET1.12 with its default settings give the best global agreement to the data. They generate LHC predictions with ~30% difference for min bias, and ~ a factor of 2 for UE distributions • More activity in the UE than predicted for an average min bias event! PYTHIA6.214-tuned predicts an increase (~ a factor of 2) in this activity when extrapolating from Tevatron to LHC, whereas PHOJET1.12 suggests the ratio UE/min bias will remain the same Marina Cobal - Atlas Week, Oct 2004

  28. Top: Resonances

  29. New study on Resonances • Many theoretical models include resonances decaying to ttbar • SM Higgs(but BR smaller with respect to the WW and ZZ decays) • MSSM Higgs(H/A, if mH,mA>2mt, BR(H/A→tt)≈1 for tanβ≈1) • Technicolor Models, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons” production, […] • Generic resonance with 350 GeV<MX<5 TeV ; X < det and X > det • Signal observation above continuum BKG within a 2detmass window  =0.9545 fraction of signal within window • Signal must have • a stat significance > 5  • must contains ≥ 10 evts Analysis : determination of X, tt and (fraction of BKG in window) E. Cogneras, D. Pallin Marina Cobal - Atlas Week, Oct 2004

  30. EfficiencyDetector resolution • Low efficiency above MX ~2 TeV • Jet overlap • Muon less isolated • Need to look for an alternative method for high MX • As for high pt jet method used in Top mass measurement • No isolated muon in the preselection (and trigger menu)

  31. ttbar continuum • Analysis repeated for standard model (the BKG!) • Effect of jet calibration in the continuum: • Resonance mass shift (mtt) all jets mis-cal. (mtt)= 0.61 10-2 mtt - 0.48 per % of mis-calib. b jets mis-cal (mtt)= 0.36 10-2 mtt - 0.21 per % of mis-calib. • Typically for a 1TeV resonnance (mtt)= 5.6 GeV (all jets) (mtt)= 3.4 GeV (b jets) Marina Cobal - Atlas Week, Oct 2004

  32. Discovery potential Resonance width x < det • Resonance width x = 2 det • Results close to TDR. For 300 fb-1 • MX = 5OO GeV/c2 discovery if (.Br)> 1500 fb Needs to investigate new • MX = 1 TeV/c2 discovery if (.Br)> 650 fb methods to improve at • MX > 3 TeV/c2 discovery if (.Br)> 11 fb high mass Marina Cobal - Atlas Week, Oct 2004

  33. Top: Spin Correlation

  34. E. Monnier, P. Pralavorio, F. Hubaut Top Spin Correlation • Since no hadronisation: daughter keep spin info • Study in semi-leptonic and di-leptonic • Spin analyser: • Leptonic: lepton • Hadronic: (W, b) or least energetic jet (lej) • Interesting angles: • Θ1 (Θ2) : angle between chosen spin axis and spin analyzer direction in the t(t) rest frame. Spin axis is t(t) direction in the parton c.m.s. (helicity basis) • φ : angle between spin analyzers direction in the t(t) rest frame Marina Cobal - Atlas Week, Oct 2004

  35. Variables C = degree of spin correlation in the helicity base Unbiased estimator of C : -9 < cos q1 cos q2 > = 0.16 Unbiased estimator of D : -3 < cos φ > = -0.11 • TopReX 4.05(SM): LO spin correlation simulation • Pythia 6.221(NC): CTEQ5L and ISR-FSR • AlpGen: used for W+jets background • Tauola+Photos 2.6: t decay and radiative corrections • Atlfast 2.60: ATLAS fast simulation and reconstruction Marina Cobal - Atlas Week, Oct 2004

  36. C extraction Results for S + B( stat. systerrors) : 80500 S, S/B=15 • C(lej) = 0.21  0.015  0.04 = ~ 5 σ from 0 • D(lej) = -0.12  0.01  0.02 = ~ 5 σ from 0 • Study with full simulation just started scientific note Marina Cobal - Atlas Week, Oct 2004

  37. Top: Commissioning(see talk of S. Bentvelsen)

  38. S. Bentvelsen, M. Cobal Scenarios under study • pp collisions • What variations in predictions of t-tbar – which generator to use? • Underlying event parameterization • Background estimation from MC • Try to be as independent from MC as possible. • Detector pessimistic scenarios • Partly or non-working b-tagging at startup • Dead regions in the LArg • Jet energy scale • Use data to check data • Software tools • Many studies (not all!) only in fast simulation It is clear we need to redo most important studies with full simulation • Estimate top physics potential during first few months of running Marina Cobal - Atlas Week, Oct 2004

  39. Status of top event generators • ‘Old’ Leading Order MC: • Pythia: full standalone MC • Herwig: full standalone MC • TopRex (include spin correlations – interfaced to Pythia) • ‘New’ NLO QCD calculations implemented in MC • MC@NLO – interfaced to Herwig shower and fragmentation • This is relevant theoretical improvement • Superseeds the old Pythia and Herwig MC’s. • Validation done for this generator • Currently DC2 processes 106 MC@NLO t-tbar events • Crucial for us to analyse these • Waiting for Tier0 exercise to obtain reconstructed objects Marina Cobal - Atlas Week, Oct 2004

  40. Background events • Top physics background • Mistags or fake tags • Non-W (QCD) • W+jets, Wbbar, Wccbar • Wc • WW,WZ,ZZ • Z  tt • Single top • AlpGen W+4 jets samples produced • Very CPU intense (NIKHEF grid) • Un-weighting to W lepton (e,,) decay • Production: • Effective : 2430 pb • 380740 unweighted events generated (2.6 10-5 efficiency) • 3.41% (13002) events pass first selection • ~ 150 pb-1 W+4jet background available Largest background is W+4 jet. This background cannot be simulated by Pythia or Herwig shower process. Dedicated generator needed: e.g. AlpGen. Large uncertainties in rate Ultimately, get this rate from data itself. For example, measure Z+4 jets rate in data, and determine ratio (Z+4 jets)/(W+4 jets) from MC W+4 extra light jets Jet: Pt>10, ||<2.5, R>0.4 No lepton cuts Initial grid: 200000*3 Events: 150·106 Jobs: 98 ~1.5 1010 events! Marina Cobal - Atlas Week, Oct 2004

  41. Selection: Isolated lepton with PT>20 GeV Exactly 4 jets (R=0.4) with PT>40 GeV Reconstruction: Select 3 jets with maximal resulting PT Non b-tag tops t  bjj V. Kostiouchine M (bjj) Marina Cobal - Atlas Week, Oct 2004

  42. Extraction of top signal • Fit to signal and background • Gaussian signal • 4th order polynomal Chebechev background • In this fit the width of top is fixed at 12 GeV 150 pb-1 Extract cross section and Mtop? Need full simulation!! Marina Cobal - Atlas Week, Oct 2004

  43. Lower luminosity? • Go down to 30 pb-1 • Both W and T peaks already observable • See something! 30 pb-1 Marina Cobal - Atlas Week, Oct 2004

  44. More efforts on.. • Mtt reconstruction • Top mass reconstruction using full simulation • (“In situ”) W-calibration studies • Better evaluation of the FSR systematics in the Mtop reconstruction • Single top studies… • Involvement in the DC2 validation (our group has a link-person dedicated to this since 1 year) Marina Cobal - Atlas Week, Oct 2004

  45. SM Group: Priorities for November & Rome LHC Physics Environment: • Parton Density Functions • studies just beginning. Expect results for Rome. • understand how PDF knowledge will evolve in first years of data • (i.e. PDF is largest syst. uncertainty in many studies, but will this be true after LHC further constrains them?) • Underlying event need uniform tunings for Pythia / Jimmy • timescale: DC2. Presentation in November. • important e.g. for studies that use MC@NLO for signal, and Pythia for backgrounds Fundamental SM Measurements • W-mass, Drell-Yan, and AFB in Z0e+e- • fast simulation only thus far specific performance issues need full sim. • are performance assumptions realistic? • focus on lepton energy scale (dominates W-mass) • forward electron tagging (for AFB) Marina Cobal - Atlas Week, Oct 2004

  46. Understand the interplay between using the top signal as tool to improve the understanding of the detector (b-tagging, jet E scale, ID, etc..) and top precision measurements More studies on the QCD W+jet events Perform a preliminary cross section study for November. Finalize it for Rome Present a “final” Mtt analysis for Rome Draft note on commissioning with top events ready before Rome Top Group: Priorities for November & Rome Marina Cobal - Atlas Week, Oct 2004

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